1. Field of the Invention
The present invention relates generally to radiation therapy devices, and more particularly, to the verification of treatment fields of radiation therapy devices.
2. Description of the Related Art
Conventional radiation therapy typically involves directing a radiation beam at a tumor in a patient to deliver a predetermined dose of therapeutic radiation to the tumor according to an established treatment plan. This is typically accomplished using a radiation therapy device such as the device described in U.S. Pat. No. 5,668,847 issued Sep. 16, 1997 to Hernandez, the contents of which are incorporated herein for all purposes.
The radiotherapy treatment of tumors involves three-dimensional treatment volumes which typically include segments of normal, healthy tissue and organs. Healthy tissue and organs are often in the treatment path of the radiation beam. This complicates treatment, because the healthy tissue and organs must be taken into account when delivering a dose of radiation to the tumor. While there is a need to minimize damage to healthy tissue and organs, there is an equally important need to ensure that the tumor receives an adequately high dose of radiation. Cure rates for many tumors are a sensitive function of the dose they receive. Therefore, it is important to closely match the radiation beam""s shape and effects with the shape and volume of the tumor being treated.
Both primary photon and primary electron beams may be used in radiation therapy. Accordingly, many existing radiation therapy devices include the ability to generate and deliver both photon and electron beams. Currently, clinical practice requires substantial manual intervention to use conformal electron treatment. Conformal photon fields typically are shaped using one or more collimating devices positioned between the source and the treatment area. Many of these photon beam collimating devices may be positioned automatically to deliver a desired photon field shape to a treatment area on a patient. Little manual intervention is required to administer photon radiation therapy.
Primary electrons are currently used on approximately 30% of all patients who undergo radiation therapy. Electron fields delivered via radiation therapy devices are typically shaped using either an off-the-shelf electron applicator (either rectangular or circular in cross-section) or a custom cutout formed of Cerrobend(copyright). Both of these beam shaping methods have limitations. Off-the-shelf electron applicators often unnecessarily irradiate portions of healthy tissue, since they do not precisely conform to the target. Custom cutouts formed of Cerrobend(copyright) are highly conformal, but are costly to make, store and require special quality assurance. The Cerrobend(copyright) material may also require special handling because of the potentially toxic metals involved. Each of these approaches to electron field shaping also suffer in that they can be inefficient to use. A radiation therapist delivering a prescribed treatment must repeatedly enter the treatment room during treatment to insert the proper cutout for each field in the therapy. This is not only inefficient, but it effectively precludes the delivery of treatments which require electron field modulation in both intensity and energy at a single gantry position.
As described in co-pending and commonly assigned U.S. patent application Ser. Nos. 09/909,589, and 09/909,513 (referenced above), Applicants have developed a radiation therapy device and electron collimator which overcome many of these difficulties associated with delivery of both electron and photon beams from a single radiation therapy device.
Many radiation therapy devices utilize portal imaging techniques to verify and record the patient tumor location. Portal images are images of the patient portal through which the therapeutic radiation passes. These images can be taken before or after treatment to ascertain that the patient position, as well as the beam shape, conform to a desired treatment plan. Photon radiation therapy is well-suited to portal imaging because photons freely pass through the patient""s body, allowing an image to be taken after the photons pass through the body.
Electron therapies, on the other hand, heretofore have not been suited to portal imaging, because electrons are not transmitted completely through the patient""s body. This characteristic of electron treatments is desirable in that it ensures that almost no dose is delivered to sensitive body structures downstream from the treatment zone; however, it makes it difficult to determine whether the beam shape and patient position are correct. Accordingly, before undertaking an electron treatment, radiation therapists typically irradiate the patient with a dose of photon radiation to capture a conventional portal image. However, this solution suffers from a number of disadvantages, including the irradiation of sensitive areas of the patient to a dose of photon radiation (which electron radiation therapy is intended to avoid), and because it is not a true record of the actual treatment which will be delivered via a potentially-differently shaped electron field, further, the patient may move during the time between delivery of the photon dose and the subsequent electron therapy.
It would be desirable to provide a system and method for electron portal imaging which overcomes the drawbacks of previous systems. It would further be desirable to provide a system and method which allows efficient, accurate, and effective verification of electron treatment fields. It would further be desirable to provide effective verification of mixed beam treatments involving the application of both primary electrons and primary photons in a single course of treatment.
To alleviate the problems inherent in the prior art, and to allow the accurate, efficient and effective delivery of photon, electron, and mixed beam radiation therapy, embodiments of the present invention provide a system and method for the verification of electron treatment fields.
According to one embodiment of the present invention, a system, method, apparatus, and means for verifying an electron treatment field include positioning an image detector, and operating said image detector to detect an image created by photons generated in the delivery of an electron treatment beam. In some embodiments, the image is manipulated to generate a representation of the electron treatment field. In some embodiments, the image detector is a flat panel imaging device, such as a device using solid state sensors. In some embodiments, amorphous silicon solid state sensors are used. In some embodiments, the image detector comprises video technology to capture an image created by photons generated in the delivery of the electron treatment beam.
According to some embodiments, the image is manipulated by determining an energy of the electron treatment beam, calculating an angular dependence of the photons on the electron treatment beam, and generating the representation of the electron treatment field based on the detected image and the angular dependence.
According to some embodiments, the image is manipulated by comparing the image to an open field image to generate an enhanced image of the electron treatment field. According to one embodiment, the detection device may be used to verify fields for primary photon and primary electron therapies as well as mixed beam therapies.
The present invention is not limited to the disclosed preferred embodiments, however, as those skilled in the art can readily adapt the teachings of the present invention to create other embodiments and applications.